A grain-oriented electrical steel sheet contains 3.1% of a Si component, and has an aggregation texture in which an orientation of crystal grains is aligned at a direction of (110)[001]. This is mainly used as an iron core of a transformer, an electric motor, a generator, other electronic devices and the like, and uses extremely excellent magnetic properties at a rolling direction.
Recently, as a high magnetic flux density grade grain-oriented electrical steel sheet is commercialized, materials having less iron loss are required. This may be approached by the following four main technical methods: i) precisely orienting the {110}<001> crystal grain orientation including an easy magnetization axis of grain-oriented electrical steel sheet at a rolling direction, ii) rendering a material to be a thin plate, iii) miniaturizing a magnetic domain by a chemical or physical process, and iv) improving surface physical properties or imparting surface tension by a chemical process such as surface treating.
The last method among the above is to improve magnetism of a material by actively improving the properties of a grain-oriented electrical steel sheet surface. As a representative example thereof, a method of removing an oxide layer inevitably produced in the course of decarbonizing-annealing, and forsterite (Mg2SiO4) film, that is a base coating layer produced by a chemical reaction of MgO slurry which is a coil fusion inhibitor may be mentioned.
However, the biggest problem of the grain-oriented electrical steel sheet from which the base coating layer is removed as such is that the surface of the manufactured material is too attractive and has low roughness. Because of this, it is difficult to form an insulation coating layer on the material, and due to the absence of a base coating layer, when a general insulation coating agent is used, an insulation level required for an ordinary grain-oriented electrical steel sheet may not be expected.